The term Sushen, rendered 肅愼, is found in Chinese records, but is annotated as Mishihase or Ashihase in Japanese language documents, which should have developed into *Mishiwase or *Ashiwase in modern Japanese if the word had survived in colloquial speech.
According to the Nihon Shoki, the Mishihase first arrived at Sado Island during the reign of Emperor Kinmei.
In 660, Japanese General Abe no Hirafu defeated the Mishihase in "Watarishima" at the request of the native inhabitants.
During the Edo period, Arai Hakuseki proposed that Watarishima was Ezo, which was later renamed Hokkaidō.
Most, including Kisao Ishizuki (1979) of the Sapporo University, suggest that the Mishihase were the Nivkhs belonging to the Okhotsk culture.